The present invention relates to the art of pumping systems, and more particularly to systems and methodologies for detecting and diagnosing pump cavitation.
Motorized pumps are employed in industry for controlling fluid flowing in a pipe, fluid level in a tank or container, or in other applications, wherein the pump receives fluid via an intake and provides fluid to an outlet at a different (e.g., higher) pressure and/or flow rate. Such pumps may thus be employed to provide outlet fluid at a desired pressure (e.g., pounds per square inch or PSI), flow rate (e.g., gallons per minute or GPM), or according to some other desired parameter associated with the performance of a system in which the pump is employed. For example, the pump may be operatively associated with a pump control system implemented via a programmable logic controller (PLC) or other type of controller coupled to a motor drive, which controls the pump motor speed in order to achieve a desired outlet fluid flow rate, and which includes I/O circuitry such as analog to digital (A/D) converters for interfacing with sensors and outputs for interfacing with actuators associated with the controlled pumping system. In such a configuration, the control algorithm in the PLC may receive process variable signals from one or more sensors associated with the pump, such as a flow meter in the outlet fluid stream, inlet (suction) pressure sensors, outlet (discharge) pressure sensors, and the like, and may make appropriate adjustments in the pump motor speed such that the desired flow rate is realized.
In conventional motorized pump control systems, the motor speed is related to the measured process variable by a control scheme or algorithm, for example, where the measured flow rate is compared with the desired flow rate (e.g., setpoint). If the measured flow rate is less than the desired or setpoint flow rate, the PLC may determine a new speed and send this new speed setpoint to the drive in the form of an analog or digital signal. The drive may then increase the motor speed to the new speed setpoint, whereby the flow rate is increased. Similarly, if the measured flow rate exceeds the desired flow rate, the motor speed may be decreased. Control logic within the control system may perform the comparison of the desired process value (e.g., flow rate setpoint) with the measured flow rate value (e.g., obtained from a flow sensor signal and converted to a digital value via a typical A/D converter), and provide a control output value, such as a desired motor speed signal, to the motor drive according to the comparison.
The control output value in this regard, may be determined according to a control algorithm, such as a proportional, integral, derivative (PID) algorithm, which provides for stable control of the pump in a given process. The motor drive thereafter provides appropriate electrical power, for example, three phase AC motor currents, to the pump motor in order to achieve the desired motor speed to effectuate the desired flow rate in the controlled process. Load fluctuations or power fluctuations which may cause the motor speed to drift from the desired, target speed are accommodated by logic internal to the drive. The motor speed is maintained in this speed-control manner based on drive logic and sensed or computed motor speed.
Motorized pump systems, however, are sometimes subjected to process disturbances, which disrupt the closed loop performance of the system. In addition, one or more components of the process may fail or become temporarily inoperative, such as when partial or complete blockage of an inlet or outlet pipe occurs, when a pipe breaks, when a coupling fails, or when a valve upstream of the pump fluid inlet or downstream of the pump discharge fluid outlet becomes frozen in a closed position. In certain cases, the form and/or nature of such disturbances or failures may prevent the motorized pump from achieving the desired process performance. For instance, where the pump cannot supply enough pressure to realize the desired outlet fluid flow rate, the control system may increase the pump motor speed to its maximum value. Where the inability of the pump to achieve such pressure is due to inadequate inlet fluid supply, partially or fully blocked outlet passage, or some other condition, the excessive speed of the pump motor may cause damage to the pump, the motor, or other system components.
Some typical process disturbance conditions associated with motorized pump systems include pump cavitation, partial or complete blockage of the inlet and/or outlet, and impeller wear or damage. Cavitation is the formation of vapor bubbles in the inlet flow regime or the suction zone of the pump, which can cause accelerated wear, and mechanical damage to pump seals, bearing and other pump components, mechanical couplings, gear trains, and motor components. This condition occurs when local pressure drops to below the vapor pressure of the liquid being pumped. These vapor bubbles collapse or implode when they enter a higher-pressure zone (e.g., at the discharge section or a higher pressure area near the impeller) of the pump, causing erosion of impeller casings as well as accelerated wear or damage to other pump components.
If a motorized pump runs for an extended period under cavitation conditions, permanent damage may occur to the pump structure and accelerated wear and deterioration of pump internal surfaces, bearings, and seals may occur. If left unchecked, this deterioration can result in pump failure, leakage of flammable or toxic fluids, or destruction of other machines or processes for example. These conditions may represent an environmental hazard and a risk to humans in the area. Thus, it is desirable to provide improved control and/or diagnostic systems for motorized pumps, which minimize or reduce the damage or wear associated with pump cavitation and other process disturbances, failures, and/or faults associated with motorized pump systems and pumping processes.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Rather, the sole purpose of this summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented hereinafter. The invention provides methods and systems for detecting cavitation in pumping systems. The methods comprise measuring pressure and flow information related to the pumping system and detecting cavitation using a classifier system, such as a neural network. The systems comprise a classifier system for detecting pump cavitation according to flow and pressure data. The invention may be employed in cavitation monitoring, as well as in control equipment associated with pumping systems, whereby pump wear and failure associated with cavitation conditions may be reduced or mitigated.
One aspect of the invention provides a system for detecting cavitation in a motorized pumping system, comprising a classifier system for detecting pump cavitation according to flow and pressure data. The classifier system may comprise a neural network receiving flow and pressure signals from flow and pressure sensors associated with the pumping system, wherein the neural network is trained using back propagation. The classifier may further receive pump speed data from a speed sensor associated with the pumping system to detect pump cavitation according to the flow, pressure, and speed data. In this manner, pump cavitation may be detected for pumping systems employing variable frequency motor drives. The neural network of the classifier system may be further adapted to determine the extent of cavitation in the pumping system, such as by providing an output according to the degree of cavitation in the pump. The neural network, moreover, may provide a cavitation signal indicative of the existence and extent of cavitation in the pumping system, wherein the cavitation signal may be used to change the operation of the pumping system according to the extent of cavitation.
According to another aspect of the present invention, there is provided a method of detecting cavitation in a pumping system having a motorized pump, comprising measuring pump flow and pressure data, and detecting pump cavitation according to the flow and pressure data using a classifier system. The classifier system may comprise a neural network trained by back propagation, which inputs pressure and flow information and outputs a classification of the existence and the extent of cavitation in the pumping system. Pump speed may also be measured and provided to the neural network, whereby pump cavitation may be detected and diagnosed at different pump speeds. The methodology may further comprise providing a cavitation signal indicative of the extent of cavitation, and changing or altering the operation of the pumping system in accordance therewith, whereby the system may be controlled to reduce or mitigate pump cavitation.